A conventional roller or bushing chain comprises alternating pairs of laterally spaced inner link plates and laterally spaced outer link plates. The inner link plates are connected by cylindrical bushings the ends of which are press-fit into the link plates, and the outer link plates are connected by connecting pins that are press fit into the outer link plates. The outer link plates are disposed in overlapping relationship with the inner link plates, and the connecting pins extend rotatably through the bushings. In the case of a roller chain, the bushings are surrounded by rollers.
Both the outer link plates and the inner link plates of the conventional chain typically have an oval shape. The distance from the pitch line, i.e. a line extending in the direction of elongation of the chain through the centers of the connecting pins, to the edges of the respective link plates is referred to as the “back height.”
If the back height of the outer link plate is equal to the back height of the inner link plate, and both plates are in sliding contact with a chain guide, the area of contact between the chain and the guide becomes large, and consequently a significant amount of power is lost on account of excessive friction. In the case of an engine timing chain, for example, excessive friction can reduce the engine's fuel efficiency.
To address the above problems, a chain disclosed in United States patent application publication No. 2010/0267504, published Oct. 21, 2010 is composed of oval inner link plates that do not contact a guide, and outer link plates having bulging ends that slide on the surface of the guide. However, because the bulged ends of the chain are shorter than the chain pitch, a straight area of an inner link plate, parallel to the direction of elongation of the chain, comes into contact with the guide surface before an adjacent outer link plate when the link plates bend about a connecting pin. Consequently, the contact area is not reduced.
In the conventional roller chain, the thickness of the outer link plate is equal to the thickness of the inner link plate. Consequently, the rigidity of the inner link plates is lower than rigidity of the outer link plates. Therefore, the outer link plates can become deformed when tension is applied to the chain. As a result, the connecting pins and the bushings are subject to wear due to localized contact, and bending of the connecting pins can result in breakage.
Another problem is that, in the conventional chain, the outer link plate can ride on a curved corner of the chain guide where the chain-engaging surface meets a chain-restraining side wall formed on the guide. When the chain rides on the curved corner of the chain guide the chain can travel in an unstable inclined condition.
Accordingly, there is a need for a power transmission chain that addresses the aforementioned problems, by reducing the contact area between the chain and the chain guide, by increasing the flow of lubricating oil to the area where the chain contacts the chain guide, thereby reducing frictional losses, by assuring stable chain travel, by preventing breakage of the connecting pins, and by suppressing wear of the chain guide.